This proposal will address the following specific aims: (1) Determine the role(s) of central GRK5 in the regulation of AT1R (Angiotensin II type 1 Receptor) expression under normal conditions and during Chronic Heart Failure (CHF). (2) Identify the mechanism(s) of modulation of central AT1R and GRK5 following Exercise Training (ExT) in CHF animals. (3) Determine the role of cytosolic and nuclear GRK5 in the transcriptional regulation of AT1R by I?B and NF-?B. In Specific Aim 1 we will induce CHF by coronary artery ligation. Overexpression of GRK5 will be targeted to the RVLM or PVN by lentiviral injection. To determine the effects of GRK5 knockdown on AT1R expression and changes in sympatho-excitation, we will utilize both commercially available GRK5 KO mice and lentiviral packaged siRNA against GRK5 that will be injected into the RVLM or PVN. Urinary excretion of norepinephrine (NE), plasma NE and Ang II will be measured in all animal groups. Arterial pressure and heart rate will be continuously recorded in order to derive additional indices of sympatho-excitation and to determine arterial baroreflex function. Sympathetic nerve activity will be directly recorded under anesthesia in terminal experiments. In all animals cardiac function will be evaluated serially by high-frequency echocardiography. In Specific Aim 2, we will induce CHF in GRK5KO mice that are either sedentary or ExT as well as utilize CHF rats in which GRK5 has been silenced in the PVN or RVLM using siRNA lentivirus. Following ExT, sympathetic and baroreflex function will be evaluated in a similar fashion as in Specific Aim 1. We will test Specific Aim 3 in CATH.a neurons, utilizing both overexpression and silencing techniques with a GRK5 plasmid and siRNA to examine the subcellular localization of AT1R, I?B, NF-?B, and GRK5 following Ang II stimulation. We will also perform parallel studies using a K215R dominant negative GRK5 construct to determine if the GRK5/AT1R/I?B/NF-?B interaction is kinase-dependent. PUBLIC HEALTH RELEVANCE: Chronic Heart Failure (CHF) is one of the leading causes of death in the United States (600,000 new diagnoses each year), and is characterized in part by increased sympathetic nerve activity mediated in part by upregulation of the Angiotensin II type 1 Receptor (AT1R). Exercise training is an accepted therapy in patients with CHF and can increase survival, decrease complications, and abrogate increases in muscle sympathetic nerve activity. Gaining a greater understanding of the regulation of AT1R both during CHF and following ExT may lead to development of therapeutics and more effective treatment of this disease.